Cosine of 2a is equal to theĬosine squared of a minus the sine squared of a. Situation, which I could rewrite as, this is equal to Of a minus the sine of a times the sine of a. Then this is just equal to cosine of a times the cosine And then we could use thisįormula right up here. Well that's just the same thingĪs the cosine of a plus a. Identity for let's say, the cosine of 2a? So the cosine of 2a. Too much because we have many more identities to show. Out, so it'll be plus sine of a times the sine of b. Sine of minus b, which is the same thing as the So that's going to be theĬosine of a times the cosine- cosine of minus b is the The cosine of a minus b is, well, you use these That the cosine of a plus b is equal to the cosine of a- youĭon't mix up the cosines and the sines in this situation. These to kind of prove a bunch of more trig identities Proved this by knowing this and this ahead of time. The sine of a minus c is equal to the sine of a timesĬ is the same thing as the cosine of c. Information to rewrite the second line up here to say that And that the sine isĬ is actually equal to minus sine of c. Looking at the graph of the cosine function, or even at Going into this video, that the cosine of minus c is equal Is another assumption that we're going to have to have Times the cosine of minus c plus the sine of minus c The sine of a plus- I'll write it this way- minus c? Which is the same thingĪs a minus c, right? Well, we could just use thisįormula up here to say well, that's equal to the sine of a The sine of- well, I'll just write it a little differently.
Sine of a times the cosine of b plus the sine of b Or to prove, are that the sine of a plus b is equal to the Videos on them and they're a little bit involved to remember Going to assume that we know because I've already made Stone, let me rerecord a video and kind of refresh That I'm in need of review myself because I was doing someĬalculus problems that required me to know this, and I haveīetter recording software now so I thought two birds with one Trigonometric identities I'm going to cover in this video. Of videos that covers what I'm going to cover, the
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